Dog Sense of Smell

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Dogs rule. Or, at least, they do when it comes to their sense of smell, which crushes that of humans. According to the Alabama Cooperative Extension System (ACES), a dog's sense of smell is about 1,000 times keener than that of their two-legged companions -- and many dog experts claim it's millions of times better -- thanks to the construction of their often-slobbery, wet schnozzes. So what, exactly, is going on in there?

A dog sniffs at scents using his nose, of course, and also his mouth, which may open in a sort of grin. His nostrils, or nares, can move independently of one another, which helps him pinpoint where a particular smell is coming from. As a dog inhales a scent, it settles into his spacious nasal cavity, which is divided into two chambers and, ACES reports, is home to more than 220 million olfactory receptors (humans have a measly 5 million). Mucus traps the scent particles inside the nasal chambers while the olfactory receptors process them. Additional particles are trapped in the mucus on the exterior surface of his nose.

Sometimes, it takes more than one sniff for a dog to accumulate enough odor molecules to identify a smell. When the dog needs to exhale, air is forced out the side of his nostrils, allowing him to continue smelling the odors he's currently sniffing.

Dogs possess another olfactory chamber called Jacobson's organ, or, scientifically, the vomeronasal organ. Tucked at the bottom of the nasal cavity, it has two fluid-filled sacs that enable dogs to smell and taste simultaneously. Puppies use it to locate their mother's milk, and even a favored teat. Adult dogs mainly use it when smelling animal pheromones in substances like urine, or those emitted when a female dog is in heat.

Top Sniffers

What all of this sniffing and processing really means is that a dog's sense of smell is his primary form of communication. And it's a phenomenal one, because dogs don't just smell odors that we can't. When a dog greets another dog through sniffing, for example, he's learning an intricate tale: what the other dog's sex is, what he ate that day, whom he interacted with, what he touched, what mood he's in and -- if it's a female -- if she's pregnant or even if she's had a false pregnancy. It's no wonder, then, that while a dog's brain is only one-tenth the size of a human brain, the portion controlling smell is 40 times larger than in humans.

So, who's top dog when it comes to sniffing? While all canines have an incredible sense of smell, some breeds -- such as bloodhounds, basset hounds and beagles -- have more highly refined sniffers. This is a result of several factors. Dogs with longer snouts, for example, can smell better simply because their noses have more olfactory glands. Bloodhounds, members of the "scent hound" canine group, also have lots of skin folds around their faces, which help to trap scent particles. And their long ears, like those of Bassets, drag on the ground, collecting more smells that can be easily swept into their noses.

Of course, dogs are individuals as well, so it's certainly possible to find a non-scent-hound who can outperform one. And as Dr. Sandi Sawchuk, a clinical instructor at the University of Wisconsin School of Veterinary Medicine, notes: "There are lots of breeds that can be trained to sniff out certain items -- for example, cadaver-sniffing dogs, drug-sniffing dogs, etc."